At present, digitization of information is proceeding, however, a state of being displayed on a display is not suitable for reading through the entire information. Therefore, although digitization is proceeding, the amount of consumption of a recording medium (paper) is increasing. Further, in order to suppress CO2 emission, it is demanded to suppress the amount of consumption of paper.
Therefore, a technique capable of recycling paper by decolorizing an image from the paper having the image formed thereon is proposed.
For example, a technique in which a plurality of reversible thermal color-developable compositions having different coloring tones and different decolorization starting temperatures are allowed to exist in paper in a state where the compositions are independently encapsulated in separate microcapsules is proposed (JP-A-2004-42635). However, the technique proposed in JP-A-2004-42635 relates to special paper in which the thermal color-developable compositions are allowed to exist, and is not a technique in which an image formed on common paper is decolorized.
Further, a pigment comprising: a composition which contains an electron-donating color-developable agent, an electron-accepting color-developing agent, a reaction medium for determining a color-developing reaction starting temperature, and a predetermined color-changing temperature regulating agent as four essential components, and reversibly changes its color according to the temperature change; and microcapsules encapsulating the composition is proposed (JP-A-2004-315735). However, the technique proposed in JP-A-2004-315735 assumes the use thereof in an ink, and therefore, the color-changing temperature is low. Further, since the four essential components are encapsulated in microcapsules, and therefore, the structure thereof is complicated.
Further, as a technique for producing an decolorizable toner, a technique in which all the ingredients are mixed and a first kneading operation is performed, and the resulting kneaded material is coarsely pulverized, and then, a second kneading operation is performed is proposed (JP-A-2000-19770). However, in the technique proposed in JP-A-2000-19770, a plurality of components such as a color-developable agent, a color-developing agent, and a decolorizing agent are handled in a solid phase, and therefore, color developing and decolorizing reactions are not prompt or sufficient.